"Early" (04-06) Exhaust valve Failures

It seems that every time the topic of early exhaust valve failures comes up, there is still a lot of debate on why it happens. I am planning to put together a post that can be used as a sticky to educate everyone why it happens, so tonight I started putting together the photos.

One of the key bits of data I need is a cross sectional micrographic photo showing the microcracking, and it will take me some time to get someone to do it. Therefore, I don't intend this post to be the final sticky. I just thought it might be of interest to the group to show the early stuff now....

To start, I have fixed two skis with dropped valves, both fresh water, one with 60 hours, the other 125 hours. (I bought these as projects) I took apart the one head and inspected the valves, and it is from this head that I came to the conclusion of corrosion-induced microcracking that caused the failure. That head and parts went into the dumpster as it was really destroyed. I have had the other complete head sitting around for a year. (I have saved it as it is fixable) It has some corrosion around the face of the valves now from sitting in a humid area, but this doesn't really affect the rest of the analysis. (remember, the exhaust system on these engines is always at 100% relative humidity!)

It is from this second head that I took the following photos.

Here is the typical exhaust valve failure, and what happens as a consequence:

As you can see from the photo above, one exhaust valve dropped, the other is still in one piece. So I pulled the valve and shot of photo of it.

The above photo says it all. This is what happens when the early valves sit in the 100% humidity of the exhaust chamber for a period of time without a protective coating of fogging oil. Notice the red arrow; this is the weld junction of the two different metals that the valve is made of. Notice that the heat effects and the corrosion effects are much different above and below this line. Also note that it is at this exact point where the exhaust valve breaks. Any pitting at this junction is critical, as this is the weakest point of the valve. ( You can also see that is it slightly narrowed down at this point, so the wall thickness is less at this point) Also note that if you run the engine after this type of rust, the color and characteristic of the rust changes with the heat. That is why the photo that the recent poster put up isn't really any use. Once you run the engine, you won't see this nasty corrosion, it changes color and evens out.

Now take a look at this next photo, after I cleaned up the valve:

Notice the deep pit at the red arrow. If this pit was located at the junction showed in the previous picture, this valve would have likely failed. It didn't, because the valve is much stronger at this point.

Here is where it gets interesting. I pulled the broken valve, and when I looked at it, I saw what appeared to be rust all over the stem:

This got me thinking; is this why some guys think that rust on the stem is the root cause? So I put the stem under the microscope, and it actually was not rust, but a coating of some sort. I was able to flake it off easily with a probe. I believe that whatever this is, was probably a side reaction to the sodium metal liberated when the valve head popped off. The broken stem still slides easily in and out of the guide.

Finally , I cleaned up the broken valve stem, and put the stem and it's unbroken sister side by side so you can see where the valve breaks.

In conclusion, the early valves break from corrosion-induced cracking at the weak point, primarily due to not fogging the valves properly before storage.

If you have an '04-early 06 ski,and have not been religiously fogging before storing or don't know the history, you have been warned.

As a side note, I bought an 08 head from a guy, that had been sitting with water in the cylinder. The intake valves and the seats were badly corroded and junk. The exhaust valves had no rust, no pitting at all. The new inconel valves don't corrode like these old ones do.

I will follow up later with the micrograph photos when I get them done.

EDIT:
Much stronger and lighter after market valves can be purchased in the forums online store at a cheaper price than OEM replacements.

Sea Dood Very good FBI work. You are correct in your findings. Most of this moisture comes from the water box. When the engine is shut off and the exhaust valve is open--this allows moisture from the water box to travel back up into the exhaust manifold and coat the stem. It does not seem to affect the intake valves that I know of. Keep us posted on your findings.

Yes, the waterbox is the source of the moisture. The exhaust chamber is always at near 100% humidity.

However, Rotax designed these engines so that when the engine shuts off, it stops at a point when all the valves are closed. They did this to keep the cylinder walls from being exposed to the high humidity conditions. So the only parts that are exposed to the moist air are the head and stem of the valve, but the part of the stem in the guide is not exposed. Note also that the valve material at the stem region doesn't corrode in the same way as the head of the valve; it seems to be more resistant to corrosion.

Do these valves apply to GTI's and GTX's? All I hear are bad valves in RXT/RXP. When were the new ones installed? I have a 2006 GTISE and a 2006 GTXSC, both with about 45 hrs, mfr dates of 3/23/06 (GTI) and 4/28/06 (GTX).

Do these valves apply to GTI's and GTX's? All I hear are bad valves in RXT/RXP. When were the new ones installed? I have a 2006 GTISE and a 2006 GTXSC, both with about 45 hrs, mfr dates of 3/23/06 (GTI) and 4/28/06 (GTX).

06 was the changeover period. You should check your numbers stamped on the valves as mentioned above.

Excellent post. I've suffered from two rear cylinder exhaust valve failures ('04 RXP). When the first one went it cracked the barrel so I got an exchange engine, but it was another '04. Despite lots of fogging after two seasons it happened again (last summer), and snapped of rear exhaust valve. This time I got the engine rebuilt, head reconditioned and new pistons plus new valves throughout, so I'm hoping the engine will last this time. I do have one further thought around the causes... I have a Riva aftermarket intake, the intake is right by the gap at the front of the seat and when the ski goes through a wave / or gets splashed, the water runs right onto the intake. When I take my air throttle valve off the butterfly is always pitted with corrosion. I do ride in the ocean but so does my friend (who has an '03 GTX 4tec), his air throttle body is always spotless, he doesn't have the aftermarket intake. So my theory is, if the sea air is pitting my throttle body then surely it's not doing the cylinder chamber any good either, let alone the valve stems. I'm either going to modify the intake so its not exposed to direct water, or look for a standard one on eBay. However, interested in other people's opinions on this...